1. Field of the Invention
The present invention relates to biotechnology, and specifically to a method for producing L-amino acids by fermentation, and more specifically to genes derived from Escherichia coli bacteria. These genes are useful for improving production of L-amino acids, for example, L-threonine, L-valine, L-proline, L-leucine, L-methionine, and L-arginine.
2. Brief Description of the Related Art
Conventionally, L-amino acids are industrially produced by fermentation methods utilizing microorganisms obtained from natural sources or mutants which have been specifically modified to enhance production of the L-amino acids.
Many techniques designed to enhance L-amino acid production have been disclosed, for example, transforming microorganisms with recombinant DNA (see, for example, U.S. Pat. No. 4,278,765). These techniques are based on increasing the activities of the enzymes involved in amino acid biosynthesis and/or desensitizing the enzymes involved in the feedback inhibition by the target L-amino acid (see, for example, Japanese Laid-open application No56-18596 (1981), WO 95/16042, U.S. Pat. Nos. 5,661,012 or 6,040,160).
Alternatively, the secretion of the target L-amino acid can be increased which can enhance the productivity of the strain producing the L-amino acid. Bacteria belonging to the genus Corynebacterium in which expression of an L-lysine secretion gene is increased (lysE gene) have been disclosed (WO 9723597A2). In addition, genes coding for the efflux proteins which act to enhance secretion of L-cysteine, L-cystine, N-acetylserine, or thiazolidine derivatives are also disclosed (U.S. Pat. No. 5,972,663).
At present, several Escherichia coli genes coding for putative membrane proteins which act to enhance L-amino acid production have been disclosed. The presence of additional copies of the rhtB gene makes bacteria more resistant to L-homoserine and enhances production of L-homoserine, L-threonine, L-alanine, L-valine and L-isoleucine (European patent application EP994190A2). The presence of additional copies of the rhtC gene makes bacteria more resistant to L-homoserine and L-threonine, and enhances production of L-homoserine, L-threonine and L-leucine (European patent application EP1013765A1). The presence of additional copies of the yahN, yeaS, yfiK, and yggA genes enhance production of L-glutamic acid, L-lysine, L-threonine L-alanine, L-histidine, L-proline, L-arginine, L-valine, and L-isoleucine (European patent application EP1016710A2). Even though the complete genome sequence of Escherichia coli strain K-12 has been disclosed (Blattner F. R., Plunkett G., Bloch C. A. et al., Science, 227, 1453-1474, 1997), the functions of many ORFs remains unknown.